Such a circuit constitutes the subject matter of the French patent application published under the No. 2 649 797 in the name of the Applicants. That application, whose contents is incorporated into the present description by reference, describes in detail the advantages of this type of detection, in particular with respect to wiring compatibility between various types of installation.
Such detection is based on the principle that a voltage appears between two phase terminals of the alternator when it is caused to rotate. The above-mentioned patent application describes an embodiment in which the voltage between the above-mentioned phases is compared with a threshold voltage, e.g. +0.6 volts. When the threshold is exceeded, a logic output of the circuit changes state to activate the regulation circuit and thereby apply the appropriate regulation current to the excitation winding of the alternator.
The present invention seeks firstly to provide a circuit which improves the reliability of inter-phase voltage detection in a manner that is extremely simple and cheap.
In addition, the above-mentioned known circuit suffers from a certain number of limitations. In particular, it can be improved with respect to immunity from interference signals, in particular at radio frequencies. Furthermore, that circuit does not reliably detect the fault situation in which there is a break in a link between the alternator and one or other of the inputs for the phase signals.
In both cases, the regulator can be put into operation when the alternator is not rotating (the engine is stopped), and this leads in particular to the vehicle battery being discharged.
The present invention also seeks to mitigate these limitations without increasing the complexity or the cost of the circuit.